Sodium-hydrogen exchangers and sodium-bicarbonate co-transporters: Ontogeny of protein expression in the rat brain

We used western blotting to examine the developmental profiles (at embryoni c day 16 and postnatal days 1, 13, 23, 33 and 105) of protein expression fo r three sodium-hydrogen exchanger isoforms (1, 2 and 4) and for a sodium-bi carbonate co-transporter in three CNS regions (cortex, cerebellum and brain stem-diencephalon). In microsomal preparations, sodium-hydrogen exchanger i soform 1 and sodium-bicarbonate co-transporter protein expression in the CN S increases gradually from embryonic day 16 (25-40% of the adult level) to postnatal day 105. In contrast, sodium-hydrogen exchanger isoform 2 and 4 e xpression reaches a maximum (three to 20 times the adult level) at around t hree to four weeks of age. There is significant regional heterogeneity in t he expression of sodium-hydrogen exchanger and sodium-bicarbonate co-transp orter proteins in the rat CNS. Sodium-hydrogen exchanger isoform 1 was high ly expressed in the brainstem-diencephalon, whereas the sodium-bicarbonate co-transporter was robustly expressed in the cerebellum and brainstem-dienc ephalon. These data indicate that the expression of sodium-hydrogen exchanger and so dium-bicarbonate co-transporter proteins varies as a function of both devel opment and specific brain region. (C) 2001 IBRO. Published by Elsevier Scie nce Ltd. All rights reserved.